Hybrid electric vehicles having an internal combustion engine combined with a motor-generator and an electrical energy storage system have been the focus of considerable attention in the automotive field, particularly in the field of passenger vehicles. Development of hybrid electric vehicle systems has only recently begun to attract significant interest in commercial and off-road vehicles, e.g., trucks and busses in Vehicle Classes 2-8, in earth-moving equipment and railroad applications, and in stationary internal combustion engine-powered installations.
U.S. patent application Ser. No. 15/378,139, assigned to the present Applicant and incorporated by reference in full herein, discloses a novel approach to providing the benefits of hybrid electric technologies in which a hybrid electric vehicle system is located at a front end of an engine, with a motor-generator being arranged in a manner that requires little or no extension of the length of the front of the vehicle. This system is referred to as a front end motor-generator or “FEMG” system.
As used in this description, the “front end” of the engine is the end opposite the end from which engine-generated torque output is transferred to the primary torque consumers, such as a vehicle's transmission and drive axles or a stationary engine installation's load, such as a pump drive. Typically, the rear end of an engine is where the engine's flywheel is located, and the front end is where components such as engine-driven accessories are located (e.g., air conditioning and compressed air compressors, engine cooling fans, coolant pumps, power steering pumps).
In this front end motor-generator system, the motor-generator is located in the front region of the engine, laterally offset to the side of the rotation axis of the engine crankshaft, and is supported on a torque transfer segment (also referred to as a “drive unit”) between the motor-generator and the region immediately in front of the front end of the engine's crankshaft. The torque transfer segment may take the form of a narrow-depth parallel shaft gearbox arranged with its input rotation axis co-axial with the engine crankshaft.
An important feature of the front end generator system is that the motor-generator exchanges torque with the engine crankshaft via the torque transfer segment and a switchable coupling (i.e., disengageable) between the torque transfer segment and the front end of the crankshaft. The switchable coupling includes an engine-side portion coupled directly to the engine crankshaft, a drive portion engageable with the engine-side portion to transfer torque therebetween, and an engagement device, preferably an axially-actuated clutch between the drive portion and the engine-side portion. The engine-side portion of the coupling includes a crankshaft vibration damper (hereafter, a “damper”), unlike a conventional crankshaft damper that traditionally has been a separate element fixed to the crankshaft as a dedicated crankshaft vibration suppression device. This arrangement enables transfer of torque between the accessory drive, the motor-generator and the engine in a flexible manner, for example, having the accessory drive being driven by different torque sources (e.g., the engine and/or the motor-generator), having the engine being the source of torque to drive the motor-generator as an electric generator, and/or having the motor-generator coupled to the engine and operated as a motor to act as a supplemental vehicle propulsion torque source.
Particularly preferably, the switchable coupling is an integrated clutch-pulley-damper unit having the clutch between the engine side damper portion and the drive portion. The drive side portion includes a drive flange configured to be coupled to the engine-end of the torque transfer segment, the drive flange also including one or more drive pulley sections on its outer circumference. This preferred configuration also has all three of the pulley, clutch and damper arranged concentrically, with at least two of these elements partially overlapping one another along their rotation axis. This arrangement results in a disengageable coupling with a greatly minimized axial depth to facilitate FEMG mounting in the space-constrained environment in front of an engine. The axial depth of the coupling may be further minimized by reducing the axial depth of the clutch, pulley and damper to a point at which the drive pulley extends concentrically around all or at least substantially all of the clutch and the engine-side damper portion of the coupling.
Alternatively, one or more of the three clutch, pulley and damper portions may be arranged co-axially with, but not axially overlapping the other portions as needed to suit the particular front end arrangements of engines from different engine suppliers. For example, in an engine application in which a belt drive is not aligned with the damper (i.e., the damper does not have belt-driving grooves about its outer circumference, such as in some Cummins® engine arrangements), the belt-driving surface of the pulley portion of the coupling need not axially overlap the damper. In other applications having belt drive surfaces on the outer circumference of the damper and a further belt drive surface on a pulley mounted in front of the damper, such as in some Detroit Diesel® engines, the coupling that would be used in place of the original damper and pulley may be arranged with both belt drive surfaces on a pulley that extends axially over the damper (i.e., the damper axially overlaps substantially all of both the damper and the clutch), or with a belt drive surface on the outer circumference of the damper, for example, to drive engine accessories that are never disconnected from the crankshaft, such as an engine coolant pump, while another other belt drive surface is located on the pulley member that extends axially over the clutch.
Previously, crankshaft dampers were typically designed with an outer portion, typically a concentric ring, resiliently connected to an inner hub of the damper directly mounted on the front end of the crankshaft. Such dampers were designed such that the inertia of the outer portion would permit the outer portion to concentrically oscillate about the inner hub at a frequency that effectively matched and offset crankshaft rotation vibrations (i.e., small angular irregularities in the crankshaft's rotation caused by “micro” accelerations and decelerations of the crankshaft associated with individual force pulses applied to the crankshaft (e.g., individual cylinder combustion events, individual cylinder compression stroke resistance, etc.). Left unaddressed, these crankshaft rotational speed oscillations can cause significant damage to the engine's internal components.
The addition of a switchable coupling, such as the clutch-pulley-damper unit disclosed in application Ser. No. 15/378,139, to the front end of a crankshaft has the potential to alter the torsional stiffness seen by the crankshaft when the switchable coupling is closed and the torque transfer segment is thereby coupled to the crankshaft. When so coupled, the torque transfer segment gear train and the attached motor-generator may present the crankshaft with an increase inertia which can impact the natural frequency of the mass elastic system. The result can be less effective damping of the crankshaft vibrations than desired.
The present invention provides a switchable coupling which addresses this problem by including a resilient portion in the clutch-pulley-damper unit that effectively isolates much of the additional inertia of the torque transfer segment and motor-generator from the engine crankshaft.
Preferably, at the point at which the drive input to the torque transfer segment is coupled to the output of the switchable coupling (in the clutch-pulley-damper unit and gearbox in application Ser. No. 15/378,139, via a male-female spline connection), a polygonal-shaped coupling is provided, with at least one of the male and female polygonal portions having area in which additional flexibility is incorporated. For example, on the male side of a triangular polygonal coupling, near each of the three corners a slot (or other geometry) may be provided that allows each corner to slightly flex when loaded by angular vibration pulses from the crankshaft. Such an arrangement would allow the male portion of the torque transfer segment-to-switchable coupling arrangement to rotate slightly relative to the female portion in response to the crankshaft vibrations. The present invention is not limited to a slot configuration, but may use any aperture geometry the provides the desired amount of resilient response to crankshaft acceleration/deceleration pulses.
With the present invention's the use of a polygonal drive arrangement with vibration-absorbing features, the crankshaft is effectively isolated from the inertia of the torque transfer segment and motor-generator by the vibration-absorbing features. The clutch-pulley-damper unit therefore may be designed in a manner that keeps its vibration response range seen by the crankshaft in the range of the crankshaft vibrations, yet ensure the crankshaft is still able to transmit its full drive torque to the torque transfer segment and the motor-generator.
The shape of the polygonal coupling is not limited to a triangular polygon, but instead may have any number of sides, as long as the polygon is modified to induce the desired coupling flexibility as in the triangular example. Moreover, the present invention is not limited to any particular shape (e.g., oval, dog-bone), as long as the vibration-absorbing portions of the shape permit the coupling to absorb circumferential vibrations while still maintaining the ability to transfer torque output from the crankshaft to the torque transfer segment, as would a splined coupling.
The polygonal coupling of the present invention is not limited to use in front end motor-generator systems, or to applications in which an internal combustion engine is present. The potential applications of the inventive polygonal coupling include any application in which torque is transferred over a rotating coupling, such as between driven and a driving shafts. Such applications include various industrial applications, such as torque transfer to and/or from an electric motor, a compressor, a pump, a gear drive, a transmission, and the like. Moreover, the present invention is not limited to internal combustion engine applications, but may be used with any form of power transmission device, such as an electric motor of a vehicle equipped with an electric drive motor.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.